1. Field of the Invention
The invention relates to a hand-guided implement.
2. Description of the Related Art
Such an implement, such as, for example, a vibratory tamper for soil compaction or an impact hammer, has a gasoline engine, but occasionally also a diesel engine or an electric motor, for the drive. Provided no electric starter is provided, the engine is normally started by actuating the pulling cable of a reversing starter. To this end, the operator takes a firm hold of the tamper with one hand, for example, while he pulls the pulling cable with the other hand. Since the throttle lever of the engine usually has to be set to full throttle for starting, the engine runs immediately at a high speed, which is often even above the operating speed. As a result, a centrifugal clutch coupling the engine to the tamping system is closed, as a result of which the tamping system is put into operation. The result of this is that the tamper performs pronounced tamping movements and can hardly be controlled by the operator, who at this moment is holding the tamper only with one hand. Operation is made even more difficult owing to the fact that a choke valve normally present at the carburetor is closed during starting, and this choke valve has to be opened again to end the starting operation. To this end, the operator must try to reach and actuate the choke lever, which is arranged at a different point from the pulling cable of the reversing starter.
An arrangement for controlling the speed of an internal combustion engine in an implement which can be guided at a handle is proposed in subsequently published DE 198 34 443, in which arrangement a detecting device has a sensor system on the handle, this sensor system being able to automatically detect whether the implement is being guided properly. If it is detected that the implement is not being guided properly, the detecting device merely enables the engine speed to be set to a safety speed below an operating speed of the internal combustion engine. In this case, the safety speed is below an engagement speed at which, for example, a centrifugal clutch of a tamper engages.
The basic idea described in DE 198 34 443 is to be further developed by the present invention. The object of the invention is therefore to specify a hand-guided implement in which dangerous working states due to uncontrolled engine speed increases are avoided and which permits easy operation.
The object is achieved according to the invention by hand-guided implements which are defined in the coordinated patent claims 1 and 2. Advantageous further developments of the invention can be gathered from the dependent claims.
In the first embodiment of the invention according to patent claim 1, a sensor device for detecting the hands of an operator and producing a corresponding handle signal is provided in a guide handle of the implement. Furthermore, a safety control is provided for evaluating the handle signal of the sensor device, detecting a starting operation of the engine and driving a speed-setting device, the speed setting being effected in accordance with the following rules: a speed increase is permitted only up to a safety speed below the operating speed when the engine is started. A speed increase is permitted up to the operating speed after a time interval detected by the safety control has expired, i.e. the previous speed limit is neutralized. The engine speed is immediately limited to the safety speed when the handle signal is absent, e.g. when the operator lets go of the guide handle.
The second embodiment of the invention as claimed in patent claim 2 is fundamentally based on the same principle as the first embodiment, although the sensor device at the guide handle has at least two sensor elements which are assigned in each case to a hand of the operator and which produce a sensor signal in each case when the associated hand is detected. In a safety control, the sensor signals are evaluated, a starting operation of the engine is detected and a speed-setting device of the engine is driven, the rules which are decisive for the driving being modified slightly compared with the first embodiment: a speed increase only up to the safety speed is likewise permitted when the engine is started. A speed increase beyond the safety speed is only possible when both sensor signals are present, that is to say when the operator holds the guide handle with both hands. The current speed is not influenced when only one sensor signal is present, i.e. the speed set previously is maintained. If the engine consequently still runs at safety speed, a speed increase to operating speed may only be effected if the operator holds the guide handle with both hands. Otherwise, the safety speed is maintained. However, if the engine is already at operating speed, the latter is also maintained even if the operator removes one hand from the guide handle and merely guides the implement with the other hand. The speed is limited to safety speed when both sensor signals are absent.
A common feature of both embodiments of the invention is that the holding of the guide handle by the hands of the operator is automatically detected without the operator himself having to become active, e.g. by actuating an additional safety or dead man""s handle. He merely has to grasp the guide handle in the normal manner. The engine speed is influenced as a function of the automatically detected holding states without the operator having to actuate the throttle lever of the engine.
Pressure-sensitive, optical, capacitive or ultrasonic sensors are suitable as sensor elements.
In an especially advantageous further development of the invention, the engine can be cut out by the safety control if a predetermined time interval which can be detected by a cut-out timing element has expired. The cut-out timing element is triggered when both sensor signals are absent. In practice, this means that the implement cuts off itself if the operator does not have his hands on the guide handle during the predetermined time interval. Therefore the operator does not have to see to it that the implement cuts out, and unnecessary and environmentally harmful idling of the implement is avoided.
In a further advantageous refinement of the invention, the speed-setting device is an ignition device of the engine, this ignition device having at least two characteristic maps. In this case, a first characteristic map is provided for the normal operation of the engine, in which the engine speed corresponds to a position of a throttle lever. This also applies in the second characteristic map within a lower speed range, although the engine speed is limited to the safety speed. Exceeding the safety speed is ruled out. The safety control then drives the ignition device by changing over between the two characteristic maps.